Match cells by what?

[Northy]

I know what your all going to say but hear me out please...

The normal way you would match cells is by run time, but in my opinion this is becoming less and less of an issue, I race off road and can not remember the last time I dumped.

If you were matching some of the new high capacity cells would you still match by run time (discharge capacity)? I am thinking that it might be better to match by charge capacity, as that way no cells get over or under charged during charging and damaged.

If the cells had diferent discharge capacities then all that would be needed would be to discharge after a race to a higher than usual voltage (eg 6 Volts), and then equalise. This way no cell is getting damaged on discharge either.

Does this make sense? Or does charge capacity tend to follow the same curve as discharge capacity and would therefore be sort of the same thing?

How about matching by voltage? Whats that all about then?

Comments welcome

G

[DCM]

erm, don't they match cells by AV discharge voltage THEN runtime. the voltage being the prime number on matching, this should mean that ALL cells peak at the same time as they should have the same peak voltage.

On a personal note, I have gone to running unmathced due to the total capacity of cells now.

[Cockerill]

Isn't most matching now done on discharge voltage

Edit - Beaten to it

[Northy]

But in my opinion I think most damage will be done to the cells during charging if the cells are not matched, don't you agreee?

We have no issue with run time, why match to that?

How can matching by AV discharge voltage mean they all peak at the same time? Wouldn't it make more sense to match by charge capacity if thats what you were trying to do?

Good comments though guys, keep 'em coming.....

[Cockerill]

Matching by Discharge volts means that in theory no cell will discharge more than another, threfore no cell will over discharge.

Whats worse over-charging or over-discharging?

If you want a charger that charges cells individually then check out http://www.spintec.nl/ICC.shtml then you will have no over charging

[Northy]

Your right Tom, but I'd say both damage cells.

As we have control over the dischrge cycle, and can do each cell individually, then wouldn't it make more sense to match by charge capacity?

See what I'm saying?

G

[Cockerill]

Yeh, now that we are not discharging the cells to anywhere near low voltages then there is low risk of over-discharging them, so why not match on charge to stop over-charging.

Good idea

[DCM]

I think a perspective check is in order.... cripes whose that handsome bloke in the mirror... ooops, wrong forum...

Realy, we are hammering these cells anyhows, these cells are designed to be charged at a much lower rate and discharged at a much lower rate, we then ask them to take current at probably 5 times they should and god knows how much more times on the discharge.

Due to this, we match our cells for performance and not longevity, so we match on discharge which gives an accurate picture of an individual cells performance as what you put in is always more than what you get out. Runtime is used by larger matchers, mainly as they can then segregate cells even more, with AV and runtime, but the prime value is the AV.

If we wanted cells to last longer than a politicians speech, go boating, lol.

[andys]

Interesting idea this Graham.

Personally i've tried various cells ranging from £60 a pack to £25 quid, and I can honestly say the cheap ones perform no differently (to me anyway).

I have bought un-matched cells for this seasons outdoor regionals, I ran them at Teesdale in the 2wd, in the mud with TR32's and still had around 1700 left in the cells !

I would be interested to see what the actual tollerences were of a given pack, i.e is an unmatched pack out in terms of matching by 10% across the 6 cells, or is it more like 1 % ?

I've tried running a couple of my un-matched packs until they dump, and I was expecting it to be like the old days of racing, where you do one or 2 laps as the car slows down gradually, but it didn't, they went off just like a matched set does, pretty much all at once.

As for charging, I keep an eye on them and trun them off before they peak on the charger if I think they are getting a bit warm, to stop any potential over-charging.

I'm not buying 'team-matched' packs anymore, as i'm convinced the marketing hype is bigger than the benefits of spending twice as much as you need to !

[Oscar]

I seem to remember reading about GP's, something like 98% of cells are within a 3% tolerance as they leave the factory. Can't remember where I saw it though...

[DCM]

I guess when running mod, it is less important, I know in 19t in tourers you can notice a slight difference, but it also all depends on how 'competitive' your racing scene is and realy, would spending another £25 on a pack of cells make you that much quicker.

[andys]

Heyup John.

If your quote of 98% in a 3% tolerence is right, that's crazy. I'm not surprised i've not heard of this before, it's not the sort of information cell matchers would want banded around ?

[DCM]

I dunno, in places like cell manufacturing, it is a climate and product controlled enviroment so that level of tolerance would be expected. Just remember the amount of cells these firms are producing for other markets, if they start to have to dump x% of cells because they fall below the minimum requirement, unit costs go up.

I mean, it is a chemical make-up, and Duracell make cells to a certain level, and if they don't reach it they don't get to the market, same for anything else, imagine shampoo coming out with a too strong a mix and burning peoples heads, same difference or philosophy.